The present invention relates to a metallic protector for the hydraulic seal surfaces located at the threaded ends of drill pipes, used for drilling of oil, gas and geothermal wells, which protect the critical hydraulic seal surfaces on the drill pipe""s side pinion and side box joints, collectively referred to as drill pipe""s female and male adapters. This protection of the seal surfaces against accidental external impacts using the metallic protectors, is provided during the final stages of drill pipe fabrication which includes sandblasting, painting and application of epoxy coating on the inside surface of the drill pipe assembly, and during transportation, handling and maneuvering in the wells.
References:
D1: GB865 175A
D2: U.S. Pat. No. 2,627,877A
D3: Partial reference information. API (American Petroleum Institute)
Wells for oil, gas and extracted geothermal heat in form of steam or liquid having elevated temperatures, are typically drilled using a drill attached to a drill pipe or drill pipe strings which consist of a number of drill pipes attached together by use of threaded joints. These joints include two seal surfaces, one on each of the joining ends of the drill pipes. These seal surfaces are located perpendicular relative to the center line of each pipe assembly and at the entrance to the threaded end of the female pipe adapter, and below the threaded end of the male pipe adapter. When two drill pipe sections are screwed together, the two seal surfaces meet and join, and when the two pipe sections are properly torqued, the two seal surface a form a joint which is typically labeled a metal to metal seal joint. This joint is herein referred to as the drill pipe hydraulic joint.
This hydraulic joint is an extremely critical interface between the drill pipe section as the drill pipe is the rotational connection between the drill bit and the wellhead motor, and also serves as a conduit to transfer a variety of chemical slurries, also called mud, to the drill bit for the purpose of lubricating, flushing drill residue back out of the drilled well, and for cooling the drill bit and the attached drill pipe string which is exposed to elevated temperatures from friction induced heat. Drilled wells can reach a depth of 6 kilometers or 3.7 miles, and the slurry pumped through the drill pipe string must reach the point of the drill bit for the above stated purposes. The pressure of the pumped slurry and thus the internal pressure of the drill pipe string, can be up to 3,000 PSI or 210 Kg/cm2. Unit pipes come in a variety of different diameters from a few inches and up to 18 inches, or 46 centimeters, and with a length of up to 60 feet, or 20 meters. Drill pipe assemblies are typically fabricated from alloy steel SAE 4137H, equivalent UNS number G41370, and have a Rockwell hardness of 30xcx9c32 HRC. The hydraulic joint between each drill pipe section must be capable of withstanding extreme pressure and high torsional loading without leaking. Any leaks across two mating seal surfaces caused by an abnormal surface condition can very rapidly destroy the threaded connection and seal surfaces by erosion caused by high velocity of the leaking and escaping fluid, and consequently, the volume of fluid reaching the drill bit is reduced and this can have adverse consequences, and the drilling fluid may eventually break the drill pipe of the point of leakage, it can be a very expensive operation to recover the drill pipe lengths already in the ground, in both terms of time and money.
A drill pipe section is normally a three piece assembly, consisting of a pipe section where the side pinion, or main adapter, is welded to one end of the pipe, and the side box, or female adapter, is welded in the other end. To preclude hydraulic seal failure of the drill piping during operation, the drill pipe fabrication is concluded with a hydraulic testing, where the drill pipe assembly is internally pressurized to a pressure of between 5,000 to 10,000 PSI or 351 to 703 Kg/cm2. Furthermore, to preserve and protect critical areas on the drill pipe assembly, caps or other devices are normally attached to the ends of the assembly to provide protection during the final treatment of sandblasting and painting, and application of epoxy coating of the inside surfaces of the assembly, and during transportation, handling and maneuvering in the well.
At the present, there exist in the market a number of thread and seal protectors having different shape, form and functions. A common type of protector comprise a bell shaped form and with internal threads for adaptation to the drill pipe""s male adapter, and having a flat compressed cardboard washer installed as an interface between the lower edge of the projector bell and the hydraulic seal surface on the drill pipe adapter. A protector plug comprising a collar being formed perpendicular to the center line of the protector and flared outward, and with external threads on the plug body for adaptation to the drill pipe""s female adapter, and having a flat compressed cardboard washer installed as an interface between the lower surface of the protector collar, and the hydraulic seal surface on the drill pipe adapter. It is generally recognized that the concept or using compressed cardboard washers as a seal surface protector, provides partial protection, only. Furthermore, these washers deteriorate under extreme weather conditions, and are considered for one time use, only.
Reference 1, patent number GB855 175A, provides a concept for a single use die-cast screw thread protector for the screwed or pin ends of oil well sucker rods, with the main objective of sealing and protecting the pin or threaded ends of the sucker rod during painting and oven drying and handling and to prevent the entry of moisture into the critical threaded area. Sucker rods are used as the interfacing connection between the reciprocating driver motor, and the pump piston in the well. Sucker rods are typically connected together using an internally threaded coupling screwed to the sucker rod""s external threaded pin ends. Sucker rod or sucker rod strings, with multiple sucker rods connected together, are operated in vertical reciprocating movement and are under pull and tensional levels of loading, which vary from moderate to extremely high, dependent on the depth of the well. Sucker rods or strings are exposed to external pressure from the pumped liquid, and there are no hydraulic leak paths within the adjoining sucker rod ends and interfacing coupling. There is a high failure rate in the industry of sucker rods in operation. The majority of the incidents are associated with threaded pin ends failure caused by metal fatigue from high pull and tensional loading, and induced operating vibrations. On the contrary, a drill pipe or drill pipe string operates at moderate to extremely high torsional loading and internal hydraulic pressure, relative to the depth of the well. The most common cause of drill pipe failure is associated with high friction loading between the drill pipe or drill pipe string and the well wall which can cause a reduction of the pipe diameter of up to 0.275 inch or 7.0 millimeter, leaks at the hydraulic joint between pipe adapter sections with consequent failure of the joint from high liquid velocity erosion, and last, stress induced metal fatigue from violent shock, torsional loading and vibrations during the drilling operation.
To alleviate some of the causes for a drill pipe and sucker rod strings failure in the well, it is imperative that precautions be employed, which includes care during the last phases of drill and sucker rods fabrication, handling and transportation to the well site. Last minute inspections of critical areas are carried out prior to the insertion of a sucker rod or drill pipe into the well. Such inspections and evaluations are commonly prone to human errors, causing unexpected situations at a well site. Precautionary measures include the use of various type of screw-on protector caps or clamp-on devices, all with the common goal of providing adequate protection of essential threads and seal areas, and to deliver the pipes and rods to the well site in an acceptable condition. The screw-on protector caps commonly remain in place on a sucker rod or drill pipe until the component is up-ended into a vertical position over the well, and the protector cap is then removed and the rod or pipe is now ready to be connected to a rod coupling or a drill pipe section located in the well. The removed protectors or protector components like washers, are commonly for single use only, and are discarded at the well site. Sucker rods and drill pipes are commonly reusable and may be transferred to another site for re-use. When a sucker rod or drill pipe is disconnected, seal and thread protection is added to the ends of such components, which may be similar in nature to what was used when the component originally arrived to the well site.
The thread protector cap described in reference D1, is for single-use only, as stated in page section 20. Per FIG. 3 and claim 1, the protector cap is for use on a screwed end of a steel rod with the objective of protecting the rod""s end threads. This described thread protector cap design includes a number of unique features which are all interrelated, which may be construed to imply that if one of the features is eliminated or significantly changed, the intended function of a protector cap which will remain securely attached to the threaded end member of rod during extreme thermal cyclic changes, may be diminished, or canceled all together.
In reference D1 FIG. 4, protector cap rim 17 extend radially outward from rod surface c. Although not specifically stated in the description and the claims, it is assumed that the inner circumferential surface of rim 17 has an intended function of centering the protector cap relative to rod surface diameter c, to establish the desired line contact relationship between edge i, which is the interface between shoulder surface b and the angular surface g, and the cap seal surface 18, and also to limit the amount of radial shift of the inside surface of rim 17 relative to surface c in this event of accidental impact on surfaces 12, 15, 16 and 17. In the fabrication shop, warehouses and in the well drilling or pumping fields, sucker rods and drill pipes are typically stored in racks in both single and multiple layers. Rack support points are typically two points supports on diameter d for sucker rods, and on the pipe diameter adjacent to the male and female adapters for drill pipe assemblies. In the event of multiple layer stacking for the sucker rods having the FIG. 1 protector cap installed at both ends of the rods, the bearing and contact point between individual rods and layer would be rim surface 17, as it represents the major diameter on the sucker rod assembly, which may have adverse effect on the sealing function features. Die-cast alloys such as zine are known to have relatively soft surface condition and acceptable structural rigidity but being fragile, having moderate to low yield strength. In the extreme event of high stack loading on lower layers protector cap""s rim 17, the rim could collapse and break. In a second postulated scenario, where the flared and concaved protector cap surface 16 is exposed to an impact by a member having sharp edges coming from a direction going towards rim 17 and slightly off parallelism with rod center line f, where due to the form of surface 16 with the outward overhang inward rim 17, and the soft surface condition of the cap""s die-cast material, the sharp impact edge may not be repelled by surface 16 and instead bury itself into the soft die-cast cap material thus transferring the impact load to rod edge i and cap surface 18. Depending on the level of impact loading, the die-cast material may yield and break and move toward and reach the rod shoulder surface b, which could be adversely affected. Alternately, should this surface be the hydraulic seal surface on a drill pipe""s male adapter which is similar in configuration, an impact of this nature would likely render the seal surface unacceptable for use. Modifying the cap design as shown in FIG. 4, like eliminating rim 17 and have surfaces 16 and 18 extend to surface c only, and increase the radius of surface 16 to minimize the potential for the above described presumed accidental events and consequent potential damage to the protected components and surfaces, would likely compromise the intended function of the unique features such as a unique thread pitch configuration which together with the dimensional differential of the coefficient of thermal expansion of the threaded steel pin and of the die cast zinc cap having a guide rim 17, provides the sealing effect between surfaces 18 and i, and prevent the cap from unscrewing.
Pipe thread protector plug 47 in FIG. 6 of reference D2, is for internal threaded pipe ends having internal features which differ from the basic configuration of the drill pipe female adapter described in this document. The main features of reference D2""s FIG. 6 protector plug include a collar 38 rolled outward and inward 38a, 38b and 38c, terminating in lip 48 being approximately parallel with plug taper surface 39. Lip 48 when the plug is screwed and tighten into the female end of a pipe, interfaces and wedges to form a seal with inside tapered surface 34, whose major diameter is substantially larger than the major diameter of internal threads 32. Collar 38 is located in front of pipe surface 40 and provides impact protection of same to a level limited to the structural strength of collar 38. Protector plugs including collar 38 are typically fabricated for cost and economical reasons, from carbon steel sheet of gage 16 (equivalent thickness 0.060 inch to 1.50 millimeter). In the event that the collar should collapse locally from excessive impact force, the gap between surfaces 40 and 38c would be reduced to zero, and remaining kinetic energy in an impacting object would be transferred into surface 40 through 38a and 38c, and likely cause an unacceptable surface condition of surface 40. A radial gap is evident between surfaces 40 and 38c, which may preclude the retention of anticorrosion compound applied to surface 40. This crevice is also a trap for foreign matters and moisture, which if present, may create unacceptable conditions for surface 40. If the plug was to be screwed further in to close the subject radial and circumferential cap, surface 38c would eventually become in contact with surface 40 and may cause galling between the two surfaces from metal to metal friction, and possible entrapment of foreign matters. The above described observations are not construed to be negative to, what is believed, the intended use of thread protector plugs for standard and commercially available pipes and conduit pipes, but include the perspective of using the protector plug for drill pipe female adapter""s frontal hydraulic seal surface. The described conditions, and uses, and scenarios would be unacceptable for the drill pipe adapter""s hydraulic seal surface, which is typically machined to a surface finish of 63 RMS or better, which is the only acceptable surface condition prior to use in a drill well.
The present invention relates to a projector cap for protecting the critical frontal hydraulic seal surface of the side pinion, or drill pipe upset, on a drill pipe assembly, also referred to herein as the drill pipe male adapter. The protector cap is a screw-on type having internal threads in form and pitch equal in the external threads on the threaded end of the drill pipe adapter. Threaded ends of drill pipes are commonly threads in accordance with the specifications of API (American Petroleum Institute), or may be of a type typically referred to as premium threads which are special threads developed by the industry, which are often patented proprietary threads. Threads in the above stated categories are either straight or taper types. The cap is bell shaped in form with an upper straight or tapered cylindrical section which includes the internal threads, and terminating in a closed end having a center penetration being a non-circular shape for insertion of a torque tool having an equal shape. The lower bell shaped section can be viewed as a circumferential skirt whose outside diameter extents to, but not beyond, the outside diameter of the drill pipe adapter. The lower inner edge of the cap bell is machined to a bevel whose surface is parallel to a beveled circumferential surface located between the outer diameter and the frontal hydraulic seal surface on the drill pipe adapter. The internal threads in the protector cap are intentionally machined to a loose fit relationship with the external threads on the male adapter for the purpose of preventing thread galling, and also to provide axial thread to thread clearances between the threaded member on the adapter and the cap. The material of the protector cap is typically, but not limited to, SAE 1006GH, equivalent UNS number G10060, having a Rockwell hardness of 40xcx9c45 HRB. The minimum sheet metal thickness is typically gage number 12 or 0.105 inch, per manufacturers standard gages for steel. The sheet metal is typically stamped to circular blanks in a gap frame press followed by a single or multiple shell drawn process in a gap frame or hydraulic press, depending on protector cap length and diameter. The shell drawn process is followed by internal threading and machining of the inner bevel of the bell formed skirt. These fabrication processes, including production material, and associated tooling and tooling maintenance, are known to be very economical and cost competitive with the high cost of injection molding tooling such as die-casting, but dependent and relative to the quantity of a production run or batch. Furthermore, as thread cutting is commonly performed on semiautomatic lathes or numerical control (NC) automatic lathes and thread grinding machines, as opposed to the use of cutting threads using taps and dies, a production run of for example a three inch diameter protector cap can be divided into an unlimited number of caps having different thread forms and pitches, by a quick change or reforming of a single bit cutting tool, or a change or reforming of a grinding wheel, followed by a change in the tool feed spindle""s gear configuration or data input to the NC machine to obtain the desired thread pitch. Thread cutting in the protector cap is normally from a single to three passes cutting process, due to the shallow thread depth and loose machining tolerances required to obtain the desired loose fit with the threaded end on the drill pipe adapter. A change-over to a different thread form or pitch, or both, including proprietary forms and pitches, can normally be executed in a matter of hours. A similar scenario for the protector cap in reference D1, would as a minimum, require retooling between each different thread form, pitch or both by replacing the inner core, representing the internal threads, in the injection die-cast form. The worst case scenario would require an individual injection form for each unknown size, thread form and pitch combination.
The shell drawing process for the protector cap together with the convex, rather than concave, shape and configuration adds considerable strength, rigidity and metal hardness to the protector cap unit. When the cap is installed and torqued and prestressed to the drill pipe""s adapter and with established contact between the thread to thread surfaces, and the two parallel surfaces of the lower inner bevel on the cap bell skirt, and the outer bevel on the adapter located between the outside diameter of the adapter and the adapter""s hydraulic seal surface, the protector cap provides a complete enclosure of the adapter end, including the critical hydraulic seal surface. The described cap configuration and as installed and secured on the drill pipe""s male adapter, provides for a reusable adapter hydraulic seal surface protector, as due to the rigidity of the cap, essential features such as external diameters and bevel seal surfaces, remain unchanged from normal use and exposure, having novel features including a smooth external contour with improved capability to repel an impacting object, specifically objects having sharp edges or pointed features, a one piece component having an outside diameter being the same or less than the outside diameter of the connecting drill pipe adapter diameter, which allow for multiple layer stacking in fabrication shop, warehouse or drill site""s storage racks, an improved integrated material strength, hardness and rigidity to resist the most common types of handling impacts from a variety of different directions, and having a radially wide and axially deep annular void which serves as a buffer zone for the cap bell and space for accidental deflection and intrusion of cap bell material and other intruding objects into the vicinity of the adapter seal surfaces, with the main objective of providing optimum protection of the drill pipe adapter""s critical hydraulic seal surface. These features are different from the thread protector cap in reference D1 whose primary functions include the strength of collar 38. Protector plugs including collar 38 are typically fabricated for cost and surface 18 which preclude the entry of moisture and other matters into the threaded pin area during extreme thermal cycling, using a unique thread pitch configuration which together with the dimensional differential of the coefficient of thermal expansion of the threaded steel pin and the die-cast zinc protector cap, which creates a tight seal between rod and bevel edge i and cap seal surface 18, with the action of plastically deforming the soft material of surface 18 to the harder material of bevel edge i. This plastic deformation and permanent impregnation of the bevel edge i into surface 18 causes an increase of the material hardness in the deformed area, which will render the protector cap unfit for re-use. The protector cap configuration shown in FIG. 4 with the claimed thread pitch of 10xc2xd threads per inch, the convex, corner and overhang surfaces and together with the features described previously, provide protection for the sucker rod""s threads on the end pin, and also limits permanent radial deflection of the end pin from impact forces. It is not obvious that this protector cap configuration is adaptable to the threaded pin and of a drill pipe assembly with its included variety of thread forms and thread pitch including a combination of taper and straight threaded adapter ends, and will provide the desired protection of the drill pipe adapter""s hydraulic seal surface.
Another part of the invention relates to a protector end plug designed for the protection of the critical frontal hydraulic seal surface of the side box joint, or drill pipe upset, on a drill pipe assembly, also referred to herein as the drill pipe female adapter. The protector plug has the same characteristics as for the described protector cap for the drill pipe""s male adapter, in the specific areas of type and grade of material, thread configurations and included loose fit tolerances, material hardness and thickness and the specified fabrication processes. The protector plug is a shell drawn single component having a lower straight or tapered cylindrical section terminating in a closed end having a center penetration having a non-circular shape for insertion of a torque tool having an equal shape. The upper edge of the cylindrical section has a drawn collar extending outward, from the cylinder""s outside diameter, and is also drawn downward into an angular configuration relative to the cylinder""s top or horizontal surface. A large radius is incorporated and interfaces the outward and angular drawn collar and the upper end of the drawn cylinder. The diameter of the outer edge of the angular shaped collar is sized to extend, but not beyond, the outside diameter of the drill pipe female adapter. The inner surface and bevel of the angular collar is formed and machined to an angle being parallel to a beveled circumferential surface located between the outer diameter and the frontal hydraulic seal surface on the drill pipe""s female adapter. The external surface of the cylindrical shell shaped plug includes loose fitting threads in form and pitch equal to the inside machined threads in a drill pipe""s female adapter. When the plug is installed and torqued and prestressed to the drill pipe""s adapter end, with established contact between the thread to thread surfaces, and the two parallel surfaces of the inner bevel of the upper shell collar, and the outer bevel on the adapter located between the outside surface of the adapter and the adapter""s hydraulic seal surface, the protector plug provides a complete enclosure of the adapter end, including the critical hydraulic seal surface. The described end plug configuration and as installed and secured on the drill pipe""s female adapter, provides for a reusable adapter hydraulic seal surface protector, as due to the rigidity of the plug and integrated angular collar, essential features, such as external diameters and bevel surfaces, remain unchanged from normal use and exposure, having novel features including a smooth external contour and low profile with improved capability to repel an impacting object, specifically objects having sharp edges and pointed features, a one piece component having an outside diameter being the same or less than the outside diameter of the connecting drill pipe adapter diameter, which allow for multiple layer stacking in fabrication shop, warehouse or drill site""s storage racks, an improved integrated material strength, hardness and rigidity to resist the most common types of handling impacts from a variety of different directions, and having a radially wide and axially deep annular void which serves as a buffer zone of the frontal end of the protector plug, and space for accidental deflection of and intrusion of frontal end plug material and other intruding objects into the vicinity of the adapter seal surface, with the main objective of providing optimum protection of the drill pipe adapter""s critical hydraulic seal surface. The thread protector plug in FIG. 6 of reference D2, may not provide the required hydraulic seal surface protection, as described previously, due to, what is believed, an unacceptable configuration including features which may cause detrimental damage to the hydraulic seal surface.